Red Bull had V6 Renault concerns in 2012

Christian Horner says Renault's current predicament is all the more frustrating as Red Bull raised concerns about its V6 project at the end of the 2012 season.

Mercedes has stolen a march on its rivals this year, with Renault lagging behind from the very first pre-season test in Jerez. Despite having reservations about the imminent change in regulations after securing its third constructors' and drivers' titles in 2012, Horner says Red Bull had no idea just how far off the pace Renault would be in 2014.

"We raised our concerns as far back as the end of 2012 because we were concerned with the direction the project was going in. Obviously designing and developing engines isn't our core confidence, nor should it be, we're a chassis manufacturer and an entrant in the Formula One world championship and I don't think any of us could have envisaged Renault would be as far behind as they have been.

"But they are working hard to close that gap down ... Renault have got to get it together. They're not in Formula One to make up the numbers."

Given the nature of competition Horner says Renault can be excused for falling behind in the first year of the V6 era but insists the trend cannot continue in 2015.

"I think we have to acknowledge that Mercedes have done a very good job and Ferrari are probably slightly ahead of Renault at the moment, but probably both grouped fairly closely together. It's only Mercedes which is the standout power unit and as a result all of their teams are performing very well, at least most of them are. It's the nature of competition of when you are presented with a set of rules how you interpret those rules. Mercedes have done a great job and Renault have done a lesser job and it's their job to catch up."

Horner insists Red Bull has not given up on its partnership with Renault and says continuing with the French manufacturer would be in the team's best interests.

"I would be very surprised if Mercedes were prepared to give us an engine. Ferrari obviously have a customer engine but we want to work as a works partner, [Renault] for the longer term offers us the best chance of success. We've enjoyed a huge amount of success with Renault, we've won nearly 50 GP and won eight world championships with them. No-one is giving up on anything but where they are is not right."